Retinoid-related orphan receptors (RORs) are transcription factors which belong to the steroid hormone nuclear receptor superfamily (Jetten & Joo (2006) Adv. Dev. Biol. 16:313-355). The ROR family consists of three members, ROR alpha (RORα), ROR beta (RORβ) and ROR gamma (RORγ), each encoded by a separate gene (RORA, RORB and RORC, respectively). RORs contain four principal domains shared by the majority of nuclear receptors: an N-terminal A/B domain, a DNA-binding domain, a hinge domain, and a ligand binding domain. Each ROR gene generates several isoforms which differ only in their N-terminal A/B domain. Two isoforms of RORγ have been identified: RORγ1 and RORγt (also known as RORγ2). RORγ is a term used to describe both RORγ1 and/or RORγt.
While RORγ1 is expressed in a variety of tissues including thymus, muscle, kidney and liver, RORγt is exclusively expressed in the cells of the immune system. RORγt has been identified as a key regulator of Th17 cell differentiation. Th17 cells are a subset of T helper cells which produce IL-17 and other proinflammatory cytokines. Th17 cells have been shown to have key functions in several mouse autoimmune disease models including experimental autoimmune encephalomyelitis (EAE) and collagen-induced arthritis (CIA). In addition, Th17 cells or their products have been shown to be associated with the pathology of a variety of human inflammatory and autoimmune disorders including multiple sclerosis, rheumatoid arthritis, psoriasis, Crohn's disease and asthma (Jetten (2009) Nucl. Recept. Signal. 7: e003; Manel et al. (2008) Nat. Immunol. 9:641-649). The pathogenesis of chronic autoimmune diseases including multiple sclerosis and rheumatoid arthritis arises from the break in tolerance towards self-antigens and the development of auto-aggressive effector T cells infiltrating the target tissues. Studies have shown that Th17 cells are one of the important drivers of the inflammatory process in tissue-specific autoimmunity (Steinman (2008) J. Exp. Med. 205:1517-1522; Leung et al. (2010) Cell. Mol. Immunol. 7:182-189). There is evidence that Th17 cells are activated during the disease process and are responsible for recruiting other inflammatory cells types, especially neutrophils, to mediate pathology in the target tissues (Korn et al. (2009) Annu. Rev. Immunol. 27:485-517).
RORγt plays a critical role in the pathogenic responses of Th17 cells (Ivanov et al. (2006) Cell 126:1121-1133). RORγt deficient mice show very little Th17 cells. In addition, RORγt deficiency resulted in amelioration of EAE. Further support for the role of RORγt in the pathogensis of autoimmune or inflammatory diseases can be found in the following references: Jetten & Joo (2006) Adv. Dev. Biol. 16:313-355; Meier et al. (2007) Immunity 26:643-654; Aloisi & Pujol-Borrell (2006) Nat. Rev. Immunol. 6:205-217; Jager et al. (2009) J. Immunol. 183:7169-7177; Serafini et al. (2004) Brain Pathol.14:164-174; Magliozzi et al. (2007) Brain 130:1089-1104; Barnes (2008) Nat. Rev. Immunol. 8:183-192.
In light of the role RORγ plays in the pathogenesis of diseases, it is desirable to prepare compounds that modulate RORγ activity, which can be used in the treatment of diseases mediated by RORγ.